Megestrol acetate is a steroid compound known for its anti-neoplastic activity.
Kirk et al., U.S. Pat. No. 3,356,573, disclose a megestrol acetate pharmaceutical tablet preparation comprising lactose, magnesium stearate and starch. Kirk, et al, also disclose that liquid compositions of megestrol acetate can be useful but provided no details as to the composition of such formulations.
Petrow et al., U.S. Pat. No. 4,396,615, disclose a method of treating androgen-related disorders by administering 6-methyleneprogesterone derivatives concurrently with megestrol acetate. However, Petrow et al. but do not elaborate on what constitutes the megestrol acetate formulation.
Greaney et al., U.S. Pat. No. 4,370,321, disclose adjuvant therapy for the treatment of breast cancer employing megestrol acetate. However, the type or composition of the megestrol acetate formulation is not specifically described.
Labrie, U.S. Pat. No. 4,666,885, discloses combination therapy for treatment of female breast cancer comprising the administration of luteinizing hormones in combination with an anti-androgen compound such as megestrol acetate. In particular, Labrie discloses that the anti-androgens are formulated with conventional pharmaceutical excipients (e.g., spray dried lactose and magnesium stearate) into tablets or capsules for oral administration.
Labrie, U.S. Pat. No. 4,760,053 discloses methods of treating sex steroid dependent cancers by combination therapy which includes the use of megestrol acetate. However, Labrie does not describe the type or composition of pharmaceutical formulation used in the treatment.
Labrie, U.S. Pat. No. 4,775,661, discloses methods of treating female breast cancer with a combination therapy in which megestrol acetate is disclosed as a suitable steroidal anti-androgen. Labrie also discloses that megestrol acetate, as an active substance, may be mixed with binders such as polyethylene glycol and may include taste improving substances which can be worked into tablets or dragee cores.
Since the use of megestrol acetate is widespread in clinical medicine, it would be desirable to have a liquid pharmaceutical dosage in a flocculated form for use in those cases where patients are unable to swallow tablets or capsules or where a high dose would require the ingestion of a relatively large number of tablets. Unfortunately, the formulation of a flocculated suspension which is stable is difficult in the case of megestrol acetate.
Atzinger et al., U.S. Pat. No. 5,338,732, point out the distinction between a flocculated suspension and suspensions in general and point out that the stability of a flocculated suspension of a steroid such as megestrol acetate can be critically dependent on concentration. Furthermore, they also disclose that megestrol acetate flocculated suspensions are unique because what would otherwise be predictable based on the prior art teachings does not apply when the drug is megestrol acetate. For instance, it is well known in the art prior to Atzinger et al. that megestrol acetate, a hydrophobic solid, is not easily wetted by water and has a relatively high interfacial tension accentuated by entrapped air absorbed on the surface of the particle. Hence, the use of surfactants are required to provide a suspension and maintain physical stability. According to Atzinger et al., the amount and type of surfactants are particularly critical in providing a stable floc. The flocculated suspension of megestrol acetate of Atzinger et al. uses megestrol acetate micronized so that 90% of the weight of particles is below 20 microns and the mass median diameter is between 3.0 and 10 microns, and requires that the micronized particles are dispersed in water with polysorbate 80 and polyethylene glycol to reduce interfacial tension between the particle, entrapped gas and water.
According to R. A. Nash, Chap. 5, page 181, (Pharmaceutical Suspensions, Pharmaceutical Dosage Forms, Marcel Decker, New York) the usual concentration of a surfactant varies from 0.05 to 0.5% w/v and depends on the solids content intended for suspension. Examples of such suspensions are given in Table 1 which lists some currently marketed steroid suspensions (1989 Physicians Desk Reference, 43rd Edition) and the polysorbate 80 surfactant concentration.
TABLE 1 ______________________________________ Percent of Polysorbate 80 Concentration Used in Steroid Suspensions According to R.A. Nash, Chap. 5, page 181, (Pharmaceutical Suspensions, Pharmaceutical Dosage Forms, Marcel Decker, New York) Steroid Conc. Polysorbate 80 Steroid mg/ml percent w/v ______________________________________ Aristocort Forte 40 0.2 Artistospan 20 0.4 5 0.2 Cortone Acetate 25 to 50 0.4 Decadron - LA 8 0.075 Depo-Provera 100 0.184 Hydeltra-T.B.A. 20 0.1 Hydrocortone Acetate 25 to 50 0.4 Kenalog-40 40 0.04 ______________________________________
As taught by Atzinger et al., megestrol acetate suspensions prepared using polysorbate concentrations as indicated above are not stable in that deflocculation and caking occurs. Therefore, they state that in order to achieve a stable flocculated megestrol acetate suspension, polysorbate must be used at a concentration at about or less than 0.02% w/v, preferably from 0.005% to 0.015% w/v and most preferably 0.01% w/v, in combination with polyethylene glycol. At polysorbate 80 concentrations as low as 0.025% w/v, there is significant deflocculation and caking. They also state that at polysorbate concentrations at or below 0.005-0.01% w/v, a physically stable product was obtained but there is increased difficulty with respect to wetting of the micronized megestrol acetate at these low concentrations. Atzinger at al. further state that only surfactants having properties similar to polysorbate 80 can also be used. In this regard, they list polysorbate 20, 40, 60, 65 and 85 as having acceptable wetting properties.
Surprisingly, the present invention provides for different formulations of flocculated megestrol acetate suspensions which are also stable.